In the respirator art, many techniques have been used to attach filter elements to respirators. A common technique uses threads to attach the filter element to a corresponding threaded fitting on the body of the respirator; see, for example, U.S. Pat. Nos. 5,222,488, 5,063,926, 5,036,844, 5,022,901, 4,548,626, and 4,422,861. The filter elements typically possess helical or advancing spiral threads that mate with a tapped collar or socket that receives the filter element's threaded portion. Rotating the filter element in the appropriate direction allows the filter element to be attached to or removed from the respirator.
In another technique disclosed in U.S. Pat. No. 5,148,803, a bellows is used to fasten a filter element to a respirator. The bellows, together with a rigid band, form a rigid cuff that receives the filter element. The cuff is continued in an elastic sleeve, which surrounds the filter element in a gas-tight manner. To change the filter element, the sleeve is first folded back to the level of the cuff, allowing the filter element to be removed. During assembly, the filter element is inserted into the cuff, and the sleeve is then folded back over the filter element.
U.S. Pat. Nos. 5,078,132 and 5,033,465 disclose a respirator that uses edge seals to secure a filter element to an elastomeric face piece of the respirator. The filter element includes bonded activated carbon granules, and the edge seals are disposed between the filter element and the elastomeric face piece and are made of a suitable adhesive material such as a hot-melt adhesive, a hot-melt foam adhesive, or a latex adhesive.
A foam mask shell used in U.S. Pat. No. 4,856,508 for placing a filter element in a respirator. The foam mask shell possesses a collar that defines an opening for receiving the filter element. The filter element has an extension with an outside dimension approximately equal to the inside dimension of the cylindrical passage through the collar. To mount the filter element, its extension is inserted into the opening where it makes a relatively tight friction fit. When the extension is inserted into the opening, the latter expands due to flexibility of the foam material in the mask shell. To replace a filter element, it is grasped and twisted back and forth while pulling it away from the mask shell.
Insert molding is used in U.S. Pat. No. 4,790,306 to permanently secure a bonded absorbent filter element to a respirator face piece.
A plug-in frame is described in U.S. Pat. No. 4,771,771 to secure a filter cartridge in a chamber of the respirator. The filter cartridge is disposed in the chamber by seals that bear tightly against the cartridge to hold it in place. The filter cartridge can be fitted to the respirator by sliding it through an opening in the plug-in frame.
In U.S. Pat. No. 4,630,604 locking tongues are employed on a filter retainer to hold a replaceable filter element in an abutting relationship to the respirator frame. The filter member can be replaced by snapping off the filter retaining member from the frame.
A further technique is disclosed in U.S. Pat. No. 4,562,837, where the respirator is provided with a guide ring for engaging a filter housing. The guide ring is carried by a sleeve portion that defines an opening through which the gasses pass. The filter housing is slidable on the guide ring from a retracted stand-by position to an extended use position. A bellows located between the filter element and the respirator, permits movement of the filter element between its retracted stand-by position and its extended use position.
Sundstrom Safety AB of Lidingo, Sweden markets a respirator under the designation SR-62, which uses an elastomeric rubber filter retainer for accommodating a filter element. The filter element comprises a gas and vapor or particulate filter in a rigid injection molded plastic cartridge. To insert the filter element into the retainer, the retainer is stretched over the periphery of the filter element.
Although the above-discussed respirators use various techniques for securing a filter element to a respirator, these techniques have a number of drawbacks. For example, the filter elements that are threaded to the respirator typically include a housing or canister into which the filter material is retained. The cartridge's cylindrical geometry typically requires using the filter element as an appendage or external cartridge on the respirator which can interfere with a wearer's vision. Further, the threaded cartridges employ many parts which can add to the total volume of the filter element and overall weight of the respirator. In other types of designs, such as disclosed in U.S. Pat. Nos. 5,078,132, 5,033,465, and 4,790,306, the filter elements are not able to be readily replaced, and thus when the service life of the filter element has met its limit, the whole respirator is discarded as waste. In the model SR-62 respirator sold by Sundstrom, the filter element is replaceable; however, the retainer lacks physical strength relative to the filter element, and thus, like placing a rubber tire on a wheel, a number of manual manipulations are needed to place the filter element in the elastomeric rubber retainer. In addition, elastomeric materials can be relatively expensive and more difficult to process. Many of the other respirators discussed above possess the drawback of using fairly complicated systems for mounting the filter element to the respirator.